In hard disk drives, data is written to and read from magnetic recording media, herein called disks, utilizing magnetoresistive (MR) transducers commonly referred to as MR heads. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. An MR head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the MR head to the desired radial position on the surface of the rotating disk where the MR head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the MR head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the MR head and any electrical connections between the MR head and the disk drive. The slider has an air bearing surface (ABS), which allows it to fly over and maintain a uniform distance from the surface of the rotating disk. Alternatively, the slider may be designed to just barely remain in contact with the rotating disk during operation, as is disclosed in U.S. Pat. No. 6,226,151, the contents of which are incorporated herein by reference.
Typically, an MR head includes an MR read element to read recorded data from the disk and an inductive write element to write data to the disk. The read element includes a thin magnetoresistive sensor stripe sandwiched between two magnetic shields that are electrically connected together but are otherwise isolated. A constant current is passed through the sensor stripe, and the resistance of the sensor stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the disk, hence improving the spatial resolution of the read head.
Earlier MR sensors operated on the anisotropic magnetoresistive (AMR) effect in which a component of the read element resistance varied as the square of the cosine of the angle between the magnetization and the direction of sense current flowing through the read element. Most current disk drive products utilize a different, more pronounced magnetoresistive effect known as the giant magnetroresistive (GMR) or spin valve effect. This effect utilizes a layered magnetic sensor that also has a change in resistance based on the application of an external magnetic field.
Competitive pressures within the computer industry require progressively increasing storage capacity within a given footprint for a disk drive. To provide this increased storage capacity, it is necessary to increase the areal density of data stored on the disk. Increasing areal density drives other constraints. It is desirable for the read sensor to be located closer to the disk in order to compensate for the smaller flux levels provided from the smaller area on the disk where a given bit of data is recorded. The magnetic field detected by the sensor in the vicinity of the disk increases exponentially as the sensor is moved closer to the disk.
Taking on increased prominence is the recession of the read/write transducer and the surrounding aluminum oxide (Al2O3), known as pole tip recession (PTR) and alumina recession (ALR), respectively. Current read/write heads are produced by depositing a series of thin films on top of a substrate that may be composed of a harder material such as Al2O3—TiC (titanium carbon). The transducer is largely composed of materials such as nickel iron (NiFe) and is surrounded by the Al2O3. The transducer and alumina materials are significantly softer than the substrate. When the entire structure of the deposited layers on the substrate is lapped back to create the air bearing surface, the amount of alumina and transducer lapped away is greater than the amount of substrate that is lapped away. This results in an air bearing surface that is not planar. Instead, the alumina portion of the ABS is recessed relative to the substrate portion of the ABS. This is similarly the case for the portion of the transducer along the ABS. There may be some difference between the relative heights of the transducer and the alumina on the ABS due to masking, etching, and other factors. As can be appreciated, the recession of the transducer relative to the ABS increases the spacing between the transducer and the disk.
In prior art disk drives, this amount of recession was not a significant percentage of the spacing of the transducer relative to the disk. As fly heights decrease, however, in order to achieve stronger signal levels and allow for increased data density, the PTR is becoming a more significant contributor to magnetic spacing loss.
Others have attempted to minimize PTR in magnetic recording heads by modifying the various lapping attributes such as diamond size and the composition of the slurry material. In addition, others have modified various cleaning attributes that are utilized in the sputter etch cleaning process prior to carbon overcoat deposition, such as sputter etching, which uses high energy atoms to burn away organics. Different gases, pressures, and voltages have been experimented with.
Most existing magnetic recording heads have been produced with time-based lapping procedures that have less precise control than is available today. For example, in years past it may have been typical to lap away 100 angstroms of material with a precision of plus or minus 20 angstroms. In addition, it is also now possible to utilize the transducer as a sensor during the lapping operation. For example, it is possible to measure the resistance of the GMR read sensor while lapping (or during breaks in the lapping process) to determine when a desired amount of lapping has occurred so that the desired stripe height for the sensor can be achieved.
Many challenges remain in order to reduce magnetic spacing loss. It is against this background and a desire to improve on the prior art that the present invention has been developed.